github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-09-13 15:40:03 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

mm/slab, kfence, memcg: completely remove obj_ext for kfence objects

Browse Source 
We have already disabled memory allocation profiling for objects
allocated for KFENCE to avoid complexity. KFENCE allocations are rare
and there can be only CONFIG_KFENCE_NUM_OBJECTS (default to 255)
outstanding ones at any time, so they are among noise in the profiling
stats.

For the same reasons, we can stop memcg_kmem accounting of kfence
objects as their memory usage will be negligible wrt any practical
memcg limits.

This allows us simplifying the code and getting rid of
is_kfence_address() checks in various places, including slab_obj_ext()'s
usage of obj_to_index(). Instead we rely on the fact that slab_obj_exts()
will now always return 0 for a kfence object's fake slab, which makes
those places unreachable.

All we need to do to keep this assumption valid is not to allocate
obj_exts for kfence objects, so the checks need to guard
alloc_slab_obj_exts() where necessary.

Suggested-by: Harry Yoo <harry@kernel.org>
Link: https://patch.msgid.link/20260727-b4-objext_split-v3-13-c29ef0f1f257@kernel.org
Reviewed-by: Hao Li <hao.li@linux.dev>
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
This commit is contained in:
Vlastimil Babka (SUSE) 2026-07-27 14:54:07 +02:00
parent d4404b0f5b
commit a6172cca15
5 changed files with 26 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
mm/kfence/core.c
View File

@ -636,14 +636,6 @@ static unsigned long kfence_init_pool(void)
page = pfn_to_page(start_pfn + i);
__SetPageSlab(page);
#ifdef CONFIG_MEMCG
struct slab *slab = page_slab(page);
slab->obj_exts = (unsigned long)&kfence_metadata_init[i / 2 - 1].obj_exts |
MEMCG_DATA_OBJEXTS;
#ifdef CONFIG_64BIT
slab->obj_exts_needs_objcg = 1;
#endif
#endif
}
/*
@ -707,10 +699,6 @@ static unsigned long kfence_init_pool(void)
continue;
page = pfn_to_page(start_pfn + i);
#ifdef CONFIG_MEMCG
struct slab *slab = page_slab(page);
slab->obj_exts = 0;
#endif
__ClearPageSlab(page);
}

3
mm/kfence/kfence.h
View File

@ -102,9 +102,6 @@ struct kfence_metadata {
struct kfence_track free_track __guarded_by(&lock);
/* For updating alloc_covered on frees. */
u32 alloc_stack_hash __guarded_by(&lock);
#ifdef CONFIG_MEMCG
struct slabobj_ext obj_exts;
#endif
};
#define KFENCE_METADATA_SIZE PAGE_ALIGN(sizeof(struct kfence_metadata) * \

8
mm/memcontrol.c
View File

@ -3583,9 +3583,11 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
slab = virt_to_slab(p[i]);
if (!slab_obj_exts(slab) &&
alloc_slab_obj_exts(slab, s, flags, slab_alloc_flags)) {
continue;
if (!slab_obj_exts(slab)) {
if (is_kfence_address(p[i]))
continue;
if (alloc_slab_obj_exts(slab, s, flags, slab_alloc_flags))
continue;
}
/*

6
mm/slab.h
View File

@ -730,7 +730,11 @@ slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,
VM_WARN_ON_ONCE(obj_exts != slab_obj_exts(slab));
index = obj_to_index(s, slab, obj);
/*
* KFENCE objects have NULL obj_exts and thus can't reach this
* and we don't need obj_to_index()
*/
index = __obj_to_index(s, slab_address(slab), obj);
if (!obj_exts_in_object(slab))
stride = slab_obj_ext_size(slab);

31
mm/slub.c
View File

@ -2067,9 +2067,6 @@ static inline void mark_obj_codetag_empty(const void *obj)
if (!slab_obj_ext_has_codetag())
return;
if (is_kfence_address(obj))
return;
obj_slab = virt_to_slab(obj);
slab_exts = slab_obj_exts(obj_slab);
if (slab_exts) {
@ -2332,11 +2329,15 @@ static inline unsigned long
prepare_slab_obj_exts_hook(struct kmem_cache *s, struct slab *slab,
gfp_t flags, unsigned int alloc_flags, void *p)
{
if (!slab_obj_exts(slab) &&
alloc_slab_obj_exts(slab, s, flags, alloc_flags)) {
pr_warn_once("%s, %s: Failed to create slab extension vector!\n",
__func__, s->name);
return 0;
if (!slab_obj_exts(slab)) {
if (is_kfence_address(p))
return 0;
if (alloc_slab_obj_exts(slab, s, flags, alloc_flags)) {
pr_warn_once("%s, %s: Failed to create slab extension vector!\n",
__func__, s->name);
return 0;
}
}
return slab_obj_exts(slab);
@ -2361,9 +2362,6 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
if (alloc_flags & SLAB_ALLOC_NO_RECURSE)
return;
if (is_kfence_address(object))
return;
slab = virt_to_slab(object);
obj_exts = prepare_slab_obj_exts_hook(s, slab, flags, alloc_flags, object);
/*
@ -2383,7 +2381,13 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
put_slab_obj_exts(obj_exts);
} else {
alloc_tag_set_inaccurate(current->alloc_tag);
/*
* KFENCE allocations are rare and the amount of outstanding
* ones is limited to a small number so it's not worth setting
* tags as inaccurate because of them.
*/
if (!is_kfence_address(object))
alloc_tag_set_inaccurate(current->alloc_tag);
}
}
@ -2414,9 +2418,6 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
for (int i = 0; i < objects; i++) {
struct slabobj_ext *ext;
if (is_kfence_address(p[i]))
continue;
ext = slab_obj_ext(s, slab, obj_exts, p[i]);
alloc_tag_sub(slab_obj_ext_codetag_ref(slab, ext), s->size);
}